Masterin Astronomy Final - Unit 1

Radio astronomy can only be done from up in space, due to our ionosphere.

False

The opacity of the atmosphere is partially corrected via adaptive optics.

False

Which of the following is true regarding the speed of light?

It is constant for all electromagnetic waves traveling in a vacuum.

If we double the diameter of a telescope's mirror, what happens to its light-gathering ability?

Light-gathering ability quadruples.

You are in space with someone who you thought was a friend. You both dress in your space suits and go on a space walk. Your so-called-friend disconnects your tether to the space craft and gives you a shove and there you go, off into space at a constant velocity away from the space craft. While moving away from the space craft, you are in a state that is best described by which of the following laws?

Newton's First Law

Part B: These two photos show the same region of space. One of them is taken in visible light. Note that stars are obscured in Photo 2 but are much easier to see in Photo 1. Considering the properties of the different bands of the electromagnetic spectrum, which spectral region do you think was used to take each photo?

Photo 1 is infrared; Photo 2 is visible

Consider this diagram. Which statement is true?

The amplitude is 4 and the wavelength is 6.

A telescope design that uses a lens and no mirrors is a refractor.

True

Galileo found the rotation period of the Sun was approximately

a month

Part complete Two stars are in a binary. The masses of the two stars are the same. The two stars are currently separated by a distance r=1. Suppose the stars moved away from each other so that r=2. Did the gravitational force increase or decrease? By how much did the gravitational force increase or decrease? Hint: Think about the inverse square law that was introduced in Chapter 1.

decrease, 4x

When used in a single instrument to greatly enhance its resolution, the four separate mirrors of the VLT act as a(n) _____.

interferometer

The main reason that most professional research telescopes are reflectors is that

large mirrors are easier to build than large lenses.

An electron has a _____ electric charge.

negative

In the Northern Hemisphere, it is colder in the winter than in the summer because ________.

the Sun shines down at more of an angle during the winter

The blackbody curve of a star moving toward Earth would have its peak shifted

toward higher energies.

What problem does adaptive optics correct?

turbulence in the Earth's atmosphere that creates

The radiation our eyes are most sensitive to is the color

yellow-green at about 550 nm.

What is the peak wavelength emitted by a person with this temperature? Express your answer using two significant figures.

λpeak = 9.4 μm

Part C: The value of X-ray and gamma-ray astronomy is based on the fact that some of the most energetic sources in the cosmos radiate at these wavelengths. Magnetic storms in stellar atmospheres (including storms on the Sun), exploding stars and their nebular remnants, the regions surrounding neutron stars and black holes, and the innermost regions associated with active galactic nuclei characterize the highest energy, shortest wavelength regime. What would you need to obtain a successful X-ray image of a high-energy source? Check all that apply.

- A cosmic source of high temperature. - A telescope designed and built to be launched into space.

Warm temperatures in the summertime are chiefly due to which of the following reasons?

- The days are longer during the summer months. - The sunlight hits the ground more directly during the summer months.

In figure 0.19 in the textbook (Triangulation), using a longer baseline would result in

- a smaller angle at point B - a more accurate distance to the tree

Part B: Which of the following is/are true when comparing radio telesopes to optical telescopes? Select all that apply

- radio telescopes can observe objects in the daytime - radio telescopes can observe objects even when it's cloudy

Part B: The value of radio and infrared astronomy is partly based on the fact that light at these wavelengths can travel through cosmic clouds of gas and dust without being absorbed. That means astronomers can observe phenomena in our Galaxy and in other galaxies that otherwise would be hidden from view at optical and shorter wavelengths. Radio emission at centimeter-to-meter wavelengths can be effectively observed from the ground. What are other unique characteristics of radio astronomy within this wavelength range? Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.

1. At these wavelengths, it is necessary to build telescopes with very large light-collecting AREAS to obtain maps of sufficient sensitivity to faint cosmic signals. 2. At these wavelengths, it is necessary to build telescopes with very large signal-sensing BASELINES to obtain maps of sufficient detail. 3. Radio astronomers have pioneered the use of multiple telescopes working in concert that can produce maps of radio emission as detailed as optical images. These arrays of multiple telescopes are known as INTERFEROMETERS. 4. Astronomical observations at these wavelengths can be obtained even during STORMS.

Part A: Which of the following blackbody curves indicates the coldest object?

10^3 : Frequency = 6.2 x 10^13 Hz Wavelength = 4.8 um

The speed of light in a vacuum is

300,000 km/sec.

The angular resolution of an 8 inch diameter telescope is ________ times greater than that of a 2 inch diameter telescope.

4

Part B: Suppose an electron in some atom absorbs energy and transitions from level 1 up to level 4. Which of the following is a true statement regarding the electron transitions back down to level 1?

4 to 2, followed by 2 to 1, is possible. Downward transitions can be any number of levels.

The greatest distance above or below the ecliptic the Moon can move is

5.2 degrees.

Increasing the temperature of a blackbody by a factor of 3 will increase its energy by a factor of

81

Which of the following statements is correct?

Apollo-Amor objects are asteroids with orbits crossing the inner Solar System; Amor objects cross the orbit of Mars; and Apollo objects cross the orbit of Earth

Suppose you see the constellation Orion directly overhead around midnight in February. During which of the following months would it be directly overhead in the daytime (around noon)?

August

Part C: The Doppler effect produces a shifting in wavelength that is proportional to the radiating source's velocity of approach or recession. Each spectrum contains emission lines from hydrogen atoms, whose laboratory (unshifted) spectrum shows Hα at 656.3 nm. Armed with this knowledge, match each spectrum to the line-of-sight motion of the corresponding source.

Blue Shifted: C. Ha at 655.0 nm Red Shifted: A. Ha at 657.0 nm At Rest: B. Ha at 656.3 nm

The force of gravity varies with the

Both A and C are correct

In the summer we observe different constellations than in the winter. This is because ________.

Earth has moved to the other side of its orbit

The Spitzer Space Telescope (SST) is stationed far from Earth because

Earth is a heat source and the telescope must be kept very cool.

Arrange the following objects in order of increasing size.

Earth, Solar System, Galaxy, Universe

Galileo's observations of the sky were made with the naked eye.

False

Stefan's law states that the total energy radiated by a blackbody depends on the ________ power of the temperature of the blackbody.

Fourth

Electromagnetic (EM) radiation penetrates the atmosphere of Earth at what portions of the electromagnetic spectrum?

In visible, some IR, and some radio wavelengths

In what part of the spectrum does this lie?

Infrared

Part A: These two photos were taken at the same time and same location near San Jose, California. The one on the left was taken using visible light. Considering the properties of the other parts of the electromagnetic spectrum, which type of radiation do you think was able to penetrate the dust and smog to obtain the image on the right?

Infrared

The following diagrams all show the same star, but each shows a different planet orbiting the star. The diagrams are all scaled the same. (For example, you can think of the tick marks along the line that passes through the Sun and connects the nearest and farthest points in the orbit as representing distance in astronomical units (AU).) Rank the planets from left to right based on their average orbital distance from the star, from longest to shortest. (Distances are to scale, but planet and star sizes are not.)

Longest -> Shortest: - biggest circle - biggest oval - middle circle - smaller oval - smallest circle

Which of the following is true about observations at wavelengths other than optical or radio?

Most observations at wavelengths other than optical or radio need to be conducted by space-based telescopes.

Part B: The figure shows a radiating source in motion relative to an observer, producing a change in the pattern of wave crests that is received by that observer. What can you say about the change in wave properties? In particular, how do the waves detected by Observer A compare to those detected by Observer B?

Observer A detects a relative stretching between wave crests, yielding a longer wavelength and lower frequency, that is, a redshift.

Part A: A radiating source at rest with respect to an observer produces a series of wave crests that propagate outward. From this figure, how do the waves detected by Observer A compare to those detected by Observer B?

Observer A detects the same wavelength and the same frequency.

Which of the following is NOT a difference between the operation of a radio telescope and an optical reflecting telescope?

Optical reflectors have their detector placed at the prime focus, whereas radio telescopes do not.

Kepler's third law is best expressed as ________.

P 2 ~ a 3

Which of the following is a true statement (for people in the Northern Hemisphere)?

Polaris does not rise nor set

Which of the following statements does NOT apply to the structure of atoms?

Protons and electrons make up the nucleus.

The model of _____ used circular deferements and epicycles in a geocentric universe to explain planetary motions.

Ptolemy

Chromatic aberration in lenses is a result of which wave property of light?

Refraction

Part complete Chromatic aberration in lenses is a result of which wave property of light?

Refraction

Part A: Astronomical sources emit electromagnetic radiation at various wavelengths. Some sources might emit just visible and infrared radiation. Other sources might emit gamma, UV, visible, and infrared radiation. Some of that radiation travels in the direction of Earth and can be detected with the right telescopes placed in the right locations. Some wavelengths can be read in the atmosphere. However, the majority of wavelengths are either read from space or Earth's surface. Which observations would require you to launch a telescope above the Earth's atmosphere? Please drag each observing mode below into either the ground-based (Surface) zone or space-borne (Space) zone, depending on the respective observing requirements. Drag the appropriate items to their respective bins.

Space Zone: - X-ray observations - Far-infrared observations - Gamma-ray observations - Far-ultraviolet observations Surface Zone: - Radio Observations - Visible (optical) observations

Listed following are observable characteristics of equinoxes and solstices in the continental United States (which means temperate latitudes in the Northern Hemisphere). Match each characteristic to the corresponding equinox or solstice.

Spring Equinox: - the sun rises due east today, but will rise slightly north of due east tomorrow Summer Solstice: - longer day (most daylight) of the year - the noontime sun reaches its highest point of the year Fall Equinox: - the sun has declination 0 degree today, but will have a negative declination tomorrow Winter Solstice: - the Sun crosses the meridian 23.5 degrees lower in altitude than the celestial equator - the noontime Sun casts the longest shadows - sunset occurs at its farthest point south of due west for the year

Part C: Suppose a particular spectral line has a wavelength of 500 nm in the lab. If you look at the spectrum of star A, you see this line at 480 nm. Star B exhibits this line at 510 nm, and the line is measured to be at 530 nm in star C. Which of the following statements is true?

Star C is moving away from us faster than star B, star A is moving towards us.

Each of the following diagrams shows a spaceship somewhere along the way between Earth and the Moon (not to scale); the midpoint of the distance is marked to make it easier to see how the locations compare. Assume the spaceship has the same mass throughout the trip (that is, it is not burning any fuel). Rank the five positions of the spaceship from left to right based on the strength of the gravitational force that Earth exerts on the spaceship, from strongest to weakest.

Strongest Force -> weakest force: - closest to earth - right below the midpoint - on the midpoint - above the midpoint - force closest to the moon

What is this temperature in kelvins? Express your answer using two significant figures.

T = has been an amazing 310 K

What will happen to the absorption and/or emission spectral lines of an object moving away from Earth at high speed?

They will be shifted toward the red end of the spectrum.

In general, the brightest star in a given constellation is designated as alpha.

True

When an electron in a hydrogen atom drops from the second to the first excited energy state it emits a bright red emission line called hydrogen alpha.

True

Part complete I am a star and my blackbody curve shows that I emit more blue light than red light. From Wien's Law, you determined that my peak wavelength had an energy that was higher (i.e., more energetic) than that from the color violet and the length of my wave was smaller than that of blue light. Which band of the EM spectrum could I be from?

Ultraviolet

Which of the following is the best summary of Galileo's observations of the phases of Venus that directly refuted the Ptolemaic (geocentric) model?

Venus can be seen to exhibit a full phase, which is predicted not to happen in the geocentric model.

Night and day have approximately equal length at what time or times of the year?

Vernal and autumnal equinoxes

Listed following are locations and times at which different phases of the Moon are visible from Earth's Northern Hemisphere. Match these to the appropriate moon phase.

Waxing Crescent Moon: - visible near western horizon about an hour after sunset - sets 2-3 hours after the sun sets Waning Crescent Moon: - visible near eastern horizon just before sunrise - occurs about 3 days before new moon Full Moon: - rises at about the time the sun sets - occurs 14 days after the new moon - visible due south at midnight

A planet is orbiting the Sun at a distance of 29.5 AU. In finding the average period the planet orbits the Sun, which of the following equations is correct?

a=[(29.5)(29.5)](1//3)

The visible spectrum of sunlight reflected from Saturn's cold moon Titan would be expected to be

absorption spectrum.

Adding a secondary concave lens of carefully chosen different glass to the primary lens on a refractor allows

chromatic aberration to be reduced.

Part A: If you want to make a very dim object appear much brighter in an image photographed through a telescope, which of the following factors are important?

diameter of the telescope and the length of the exposure

Kepler's first law worked, where Copernicus' original heliocentric model failed, because Kepler described the orbits as

elliptical, not circular.

The Hydrogen H spectrum I am looking at has the red H-alpha line at 656.3 nm on the far left and the blue H-gamma line at 434.1 nm on the far right in the laboratory (i.e., at rest) and the background color of the spectrum is black. Is this spectrum a continuous, emission, or absorption spectrum? I compare my 0 km/s laboratory hydrogen spectrum to the hydrogen spectrum I obtained from a star I observed. I notice that the star's spectrum has its red H-alpha and blue H-gamma and H-gamma lines to the left of the red H-alpha and blue H-gamma lines in the laboratory spectrum. Is the star moving towards me on Earth or away from me on Earth?

emission, away

I'm an electron in the ground state of a Hydrogen atom. I am hit with a UV photon and I move up two levels to the second excited state. I then spontaneous drop one level down to the first excited state. As I dropped down, did I absorb a photon or emit a photon? What color photon am I?

emit, red

Retrograde motion was explained by the Greeks by inventing which of the following?

epicycles

In Figure 2.20 (Atomic Excitation) in the textbook, the total energy of the two photons emitted in the branch at the lower right

exactly equal to the energy of the UV photon absorbed at the left.

Milky Way Galaxy in EM light Part complete In your text on telescopes, we see many images of objects taken from space telescopes such as Figure 3.26 on the Cygnus loop supernova remnant as taken by the Extreme Ultraviolet Explorer Satellite. We see a black background, purple wispy debris eminating from small, white knots. Is this a true-color or false-color image? Order the colors from cold to hot as shown in the image.

false-color; black, purple, white

You observe a total lunar eclipse tonight. What is the moon phase? When did the moon rise according to your textbook?

full, 6pm

According to Newton's laws, the planets orbit the Sun due to _____.

gravity

You would like to build a large radio dish telescope. Where is the best place to put this telescope? Choose the best answer.

in the valley of mountains and far from light pollution

If Scorpius is now prominent in the summer sky, in 13,000 years it will be best seen

in the winter sky.

According to Copernicus, retrograde motion for Venus must occur around

inferior conjunction, when it passes between us and the Sun.

The time is 5 am and you cannot sleep. You go outside, and it is still dark. You see off the horizon a very bright celestial object that is not twinkling. What could you be looking at? Which object?

morning star, Mercury

Suppose you are in state of Georgia in the USA during the event shown in the image. What would you see at this time?

no eclipse

Radio telescopes would NOT represent a good choice for astronomical study of ________.

ordinary stars

Which type of telescope has the simplest light path?

prime focus reflector

Green light has a shorter wavelength than orange light. In a 5 inch telescope, green light will

provide better angular resolution than orange light

You go outside on a clear night and observe the Moon. You see the right side of the Moon lit up in a crescent shape. In six days, will the right side still be lit or will the entire moon face be lit or will the left side be lit? You call your friend in New York City and have them go outside with you to check on this sixth day later. You both have clear nights and you both see the Moon. What phase does your friend see?

right side lit, same waxing gibbous phase that you see

Galileo's observations of the phases of Venus ________.

showed that Venus had to orbit the Sun and not the Earth

In the geocentric Greek model, which of the following objects did not require an epicycle?

sun

How long would a radar signal take to complete a round-trip between Earth and Mars when the two planets are 1.3 AU apart?

t = 1300 seconds

If the rest wavelength of a certain line is 600 nm, but we observe it at 594 nm, then

the source is approaching us at 1 % of the speed of light.

According to the Zeeman effect, the splitting of a sunspot's spectral lines is due to

their magnetic fields.

If a star was the same size as our Sun, but was 81times more luminous, it must be

three times hotter than the Sun.

You are located on the Earth and in the Northern Hemisphere. It is a clear night and you see the Moon in your night sky. You see most of the right side of the Moon, but the moon phase is not full. What is the moon phase? How long since the new moon phase is this moon phase you see tonight?

waxing gibbous, 10 days

How much stronger is the gravitational pull of the Sun on Earth, at 1 AU, than it is on Saturn at 10 AU?

100

Suppose you clapped your hands 14 times in 60 seconds. What is the value for ν (commonly called nu)?

14/60

What is the field of view of your computer screen? Stand two arms distance away. Choose the closest answer.

20o

Drawing on Eratosthenes' method, if two observers are due north and south of each other and are separated by 400 km, what is the circumference of their spherical world if they see the same star on their meridian at altitudes of 23 degrees and 47 degrees respectively, and at the exact same time?

6,000 km

Stand two arms length away from your computer screen and measure the parallax using your outstretched thumb using the techniques learned in class. What parallax did you measure? What is the parallax angle? Choose the closest answers.

6o, 3o

According to Figure 0.8 in the textbook (The Zodiac), in January the Sun is in the constellation

Aquarius.

There are three general types of spectra: continuous, emission, and absorption. Each is characterized by a different distribution of the wavelengths (i.e., colors) of radiation. Sort the images of the three types of spectra into the appropriate bins. Drag each spectrum to the appropriate bin.

Continuous: - Bright rainbow spectrum Emission: - Mainly black spectrums Absorption: Duller rainbow with black lines